For example, the regulator circuit is configured to supply a stable step-down power voltage from an output terminal using an operational amplifier (e.g., see patent literature 1). According to the patent literature 1, the operational amplifier compares a reference voltage generated by a reference voltage generating circuit and a feedback voltage feeding back an output voltage of the output terminal. Then, the operational amplifier outputs the step-down power voltage from the output terminal by driving a control terminal of an output transistor. When an overcurrent flows in a power line, there is a possibility of breaking of an element or meltdown of a wiring. Therefore, a protection circuit is provided to the regulator circuit. The protection circuit of the patent literature 1 folds back a sense current by a current mirror circuit and compares the sense current and a reference current, and thereby to protect the circuit from the overcurrent.